1. Field of the Invention
The present invention generally relates to semiconductor power devices and more particularly to a semiconductor power device package having a lead frame-based integrated inductor.
2. Description of Related Art
It is well known to include a discrete inductor on the printed circuit board when implementing a power converter circuit. For example, the Analogic™ TECH 1 MHz 400 mA Step-Down Converter (AAT1143) requires the use of a discrete inductor. Power converters implemented in this way suffer the disadvantages of having higher component cost and of requiring more printed circuit board space.
Discrete inductors co-packaged with power ICs and other components are also well known. For example, the LTM®4600 DC/DC power converter available from Linear Technology Corporation of Milpitas, Calif., includes a built-in inductor in a 15 mm×15 mm×2.8 mm package. The large package size demonstrates the challenge of finding a discrete inductor small enough to be co-packaged with the power IC, yet having a large inductance, small DC resistance and large rated current capable of meeting power conversion requirements. Furthermore, utilizing a discrete inductor is not cost effective as the cost of the final package includes duplicative component assembly costs (the cost of assembling the discrete inductor and of the final package) and the additional cost of incorporating the discrete inductor in the final package.
It is known to dispose the integrated circuit die on top of the inductor to achieve smaller package sizes. As disclosed in U.S. Pat. No. 6,930,584, a microminiature power converter includes a substrate magnetic induction element on top of which is mounted the power IC. Disadvantageously, the induction element is exposed allowing the fragile substrate material to be easily damaged.
It is further known to dispose an inductor on top of an integrated circuit die such as a power converter integrated circuit die. For example, power converters available from Enpirion of Bridgewater, N.J., include a MEMS-based inductor having a thick electroplated copper spiral coil sandwiched between two planar magnetic layers and disposed over an integrated DC-DC converter. To achieve high inductance, a large die is required resulting in a high cost and a large package. Furthermore, complex processing is necessary in order to fabricate the planar magnetic layers.
Efforts directed at reducing package size include utilizing the lead frame as an element of the inductor. For example, U.S. Pat. No. 5,428,245 discloses forming an inductor winding as an integral part of the lead frame and U.S. Pat. No. 6,927,481 discloses forming inductive segments as part of the lead frame. These designs are suitable for RF applications, but lacking magnetic core material, they provide relatively small inductances that are not sufficient for power conversion applications.
There remains a need in the art for a semiconductor power device package having an integrated inductor that is simple to manufacture and that achieves improved cost performance. There is also a need for a semiconductor power device package having an integrated inductor that has a large inductance, a small DC resistance, a large rated current and a low loss, all sufficient for power conversion applications. There is a further need for a semiconductor power device package having an integrated inductor that has a relatively small size.